FolderPanel

FolderPanel

The Folder Panel: the presentation-only panel along the left edge of the Workspace that presents an open Folder Workspace's Folder Tree — its Markdown Documents as a browsable tree of Folder Entries. It is workspace-wide: unlike the Navigation Panel it is not tied to the Active Session, so it stays visible even when every Tab is closed. It is hidden until the user opens a Folder Workspace (FolderWorkspaceViewModel.IsFolderPanelVisible). It is presented as a tab of the Side Dock — alongside the Navigation Panel, so the two navigation panels share one column rather than each taking its own (INV-046).

• Class: UI.Controls.FolderPanel (derives from System.Windows.Controls.TreeView)
• Default style: src/UI/Controls/FolderPanel.xaml (merged in App.xaml)

Authored as a custom Control (a TreeView subclass plus a ResourceDictionary for its look), per the project's Control exception to the zero-code-behind rule — the same pattern as the OutlinePanel. The panel is view-only: it reads the Folder Tree and raises activation, and never mutates any document or the filesystem (INV-043).

How it works

The panel binds to a Folder Workspace through its Workspace dependency property and raises activation through its ActivateCommand:

• Listing — when Workspace changes, the panel sets its ItemsSource to FolderWorkspace.Entries (the top-level Folder Entries). A single HierarchicalDataTemplate renders each Folder Entry: its Children are the nested entries, and the node glyph (a folder or a Markdown file) is switched by a DataTrigger on the entry's Kind — the same technique the Difference Overlay uses for a Difference Line. A File entry has no children, so its row shows no Expand/Collapse chevron.
• Expand / Collapse — a Folder entry Expands and Collapses natively (its chevron is the TreeViewItem's own), showing or hiding the nested entries beneath it. This is view-only and changes no document.
• Activating — because a TreeView's SelectedItem is read-only (unlike the ListBox the OutlinePanel derives from), activation is driven from input rather than a selection change: OnMouseDoubleClick resolves the double-clicked row to its Folder Entry (via ItemsControl.ContainerFromElement) and, when it is a File, runs ActivateCommand with that entry; OnKeyDown does the same for Enter on the selected row. The Workspace routes the command to its OpenPathAsync, so activating a File opens it in a Tab — activating one already open just activates its existing Tab (INV-009). A Folder double-click is left to its native Expand/Collapse.

Properties

Property	Type	Description
Workspace	FolderWorkspace?	The Folder Workspace whose Folder Tree this panel lists; its Entries are the tree's roots.
ActivateCommand	ICommand?	Run when a File is activated (double-click or Enter), with the File's FolderEntry as its parameter.

Usage

<controls:FolderPanel Workspace="{Binding Folder.Folder}"
                      ActivateCommand="{Binding Folder.ActivateEntryCommand}" />